Fluid metering device



J1me 1964 LE ROY R. HAWK ETAL 3,

FLUID METERING DEVICE Filed Nov. 9, 1962 2/ COMP/P619360 INVENTORS LEROYR HAWK V/RG/L E. SCRIBNER ATTORNEY United States Patent 3,137,174 FLUIDMETERING DEVICE Le Roy R. Hawk, Hayward, and Virgil E. Scribner,Pleasanton, Califi, assignors to the United States of America asrepresented by the United States Atomic Energy Commission 7 Filed Nov.9, 1962, Ser. No. 236,752 1 Claim. (Cl. 73-423) This invention relatesto fluid metering devices and, in particular, to a device forperiodically injecting predeitermined volumes of fluid into a processstream.

It is often necessary to accurately meter small vol umes of a fluid intoa process stream. This situation arises in the monitoring of radioactiveeflluent streams, in

gas chromatography, and in certain phases of the pharmaceuticalindustry, e.g., controlled dilution of concentrated stock solutions. a

flows through the other. A pneumatically-actuated hypodermic syringereciprocates between the two chambers through the septum, therebytransferring measured volumes of .the injection fluid into the processstream.

The invention will be described with reference to the accompanyingdrawing, of which;

FIGURE 1 is across sectional view of the metering device at the start ofthe operating cycle,

FIGURE 2 is a partial view showing the hypodermic syringe in the filledcondition, y

FIGURE 3 is a cross-sectional view showing the syringe discharging intothe process stream,

FIGURE 4 is a schematic diagram of means to ope ate the metering devicein a predetermined motion cycle.

Referring now to FIGURE 1, there is shown an injection block 11 whichslides in a groove 12 formed in a base 13. Upper, middle, and lowercylindrical bores 14, 16,- and 17, respectively, are formed into block11. Upper bore 14 and lower bore 17 are constricted at their midpointsto form respective constrictions 18 and 19. A hypodermic syringe 21,having a piston 22 and a needle 23, is disposed within middle bore 16 sothat one end of piston 22 projects beyond block 11, and needle 23projects beyond the opposite side of the block. Doubleheaded pistons 24and 26 are disposed within bores 14 and 17 respectively, and the pistonshafts project beyond block 11 through airtight shaft seals 25 fixedthereto. Pistons 24 and 26 are disposed so that their shafts passthrough constrictions 18 and 19 respectively. The space between theheads of pistons 24 and 26 is filled with a high-viscosity oil 27.Piston 24 is actuated by compressed air admitted into bore 14 via ports28 and 29. Similarly, injection block 11 is actuated by compressed airadmitted into bore 17 via ports 31 and 32. The admission of air intoports 28, 29, 31 and 32 can be controlled by various cyclic controlmeans, e.g., solenoid valves in conjunction with a rotating electricalswitch. FIGURE 4 is a schematic diagram of apparatus for operating themetering device in a predetermined motion cycle. Compressed air isadmitted to a manifold 51' which, in turn, communicates with solenoidvalves 52, 53, 54, and 56. The outlets of the solenoid valves arerespectively connected to ports 28, 29, 31, and 32. An electrical timingmechanism 57 is connected to the electrical inputs of the solenoidvalves so as to actuate the valves in a predetermined cycle. Theelectrical timer may comprise a rotating electrical switch, or otherequivalent devices. Alternately, the admission of air into the 3,137,1747 Patented June 16, 1964 ice linked together atone end so as to move asa single unit. The stroke of piston 24 (hence, piston 22 as well) isadjusted by means of a limiting screw 33. The shaft of piston 26 isfixed relative to base 13 by means of a link 34 and a lock screw 362 Aswill be described later, the position of piston 26 relative to base 13determines the stroke of block 11;

A fluid 37 to be injected is contained within a well 38 bored into afirst flow block 39. A process stream 41 flows through a channel 42formed in a second flow block 43. Well 38 and channel 42 are connectedby a transverse channel 44, but the process stream and the injectionfluid are prevented from mixing by a self-sealing septum 46 disposedbetween flow blocks 39 and 43. Transverse channel 44 is sealed off atone end by a self-sealing partition 47. i The two flow blocks are fixedto base 13, and the entire block assembly is held together and madeliquidtight by a pressure plate 48 which is forced against the blockassembly by peripherally-spaced bolts 49. The pressure plate has acentral cutout portion so that needle 23 can pass therethrough.

For the purpose of illustrating the operation of the invention, FIGURE 1shows the apparatus at the start of the injection cycle. The syringe isempty, and the tip of needle 23 is immersed in the injection fluid 37.To start the cycle, compressed air is admitted to port 28, and port 29is opened to the atmosphere. The admitted air forces piston 24 to theright and, since piston 24 is linked to piston 22, also forces piston 22to the right which causes the syringe to fill with injection fluid 37.The stroke of piston 24, and hence the injection volume, is determinedby the position of limiting screw 33. Constriction 18 operates inconjunction with viscous oil 27 as a frictional damper to prevent piston24 from moving too rapidly under the compressed air pressure. FIG- URE 2shows the syringe in the filled condition with piston 24 in contact withscrew 33.

In the next phase of the injection cycle, compressed air is admitted toport 31, and port 32 is opened to the atmosphere. The admitted airexerts force to the right on piston 26, and to the left on the closedend of bore 17. Since piston 26 is fixed relative to base 13 by link 34and lock screw 36, the resultant force is directed to the left.Therefore, block 11 slides in groove 13 towards the left. constriction19 operates in conjunction with viscous oil 27 as a frictional damper toprevent block 11 from moving too rapidly under the compressed airpressure. The movement of the block pushes needle 23 through septum 46,and the tip of the needle is immersed in process stream 41. Compressedair is admitted to port 29, port 28 is opened to the atmosphere and, asa result, piston 22 is pushed home, thereby discharging the loadedsyringe intothe process stream. FIGURE 3 shows the apparatus at thisstage inthe injection cycle. The cycle is completed by admittingcompressed air to port 32 and opening port 31 to the atmosphere. Theresultant force directed to the right causes block 11 to slide towardsthe right in groove 13. Needle 23 is pulled back through septum 46, andthe relative positions of the components are restored to those shown inFIGURE 1.

The invention has been described in terms of injecting a fluid ofconstant composition into a process stream.

'However, the apparatus can be modified to inject a fluid Septa 46, and47 must be fabricated of a self-sealing material, otherwise thecontinuous penetration by needle 23 would result in leakage between theinjection fluid and the process stream.- Several synthetic elastomershave excellent self-sealing properties. In particular, ,Silastic rubber(a silicone rubber) has been tested as a septum material, and hasexhibited no detectable leakage after several hundred cycles ofoperation.

7 Various modifications may be made in the invention withoutdeparting'from the principle thereof, and the scope of the invention isintended to be limited only by the following claim.

What is claimed is: g A fluid metering device comprising, i (a) agroovedbase, v v (b) an injection block sli eably mounted on said grooved base,said injection block having first, second, 7 and third cylindrical boresformed therein, (0) a hypodermic syringe disposed within said secondcylindrical bore, said syringe comprising a barrel, piston, and needle,I (d) first and second double-action pistons disposed respectivelywithin said first and third cylindrical bores,

said first double-action piston being linked to said syringe piston, andsaid second double-action piston being adjustably locked to said base,

(e) valve and control means for operating said doubleacition pistons ina predetermined motion cycle,

( first and second fiow blocks fixed to said grooved base, saidfirst'and second fiow blocks having first and second fluid chambersformed therein and a channel communicating between said first and secondfluid chambers, said channel being oriented so that its longitudinalaxis is collinear with the longitudinal axis of said syringe needle,

(g) a first self-sealing elastomeric septum terminating one end of saidcommunicating channel,

(h) and a second self-sealing elastomeric septum disposed between saidfirst and'second fluidchambers and intersectingrsaid communicatingchannel so as to prevent fluids in said first and second chambers frommixing.

References Cited in the file of this patent UNITED TA ES PATENTS3,096,653 Martin et a. July 9, 1963

